The present invention relates to a micro-actuator and in particular to a microactuator using an electrostatic impact driving mechanism, and to a method of making such a microactuator.
Precision positioning techniques required in carrying out a micromachining or a micro-displacement operation has come to be ranked to take a very important position, and are sought to be higher in precision than ever.
Making good use of micromachining technologies for manufacturing a positioning device allows its bulk production in a batch process, and has an advantage of eliminating the need to assemble each device product individually while yielding products small-sized, at a low cost and with a reduced individual difference. For this reason, recent years have seen extensive researches conducted on various microactuators and microsystems for positioning (see M. Steven Rodger et al, xe2x80x9cIntricate Mechanisms-on-a-chip Enabled by 5-Level Surface Micro Machiningxe2x80x9d, Digest of Transducers ""99, Sendai, Japan, June 1999, pp. 990-993). Faced with the problem of importance that the force produced is unsatisfactory and that the movable distance is insufficient, however, micro-actuators so far proposed have had a limited extent of their applicability. For example, an impact driving mechanism using a piezoelectric element has been proposed (see Toshiro Higuchi, Masahiro Watanabe, Ken-ichi Watanabe, xe2x80x9cUltra-precision Positioning Mechanism utilizing Rapid Deformation of a Piezoelectric Elementxe2x80x9d, Journal of the Society of Precision Engineering, 54-11, 2107 (1998), which using a frictional force and an piezoelectric element, has both a very small displacement in a nanometer range and a movable distance utmost minimum in principle, but needs to be built up individually and has a limitation in miniaturization.
Further, microactuators so far proposed are poor in reliability measure such as to prevent entry of dust and moisture in air and are thus inferior in environmental reliability.
It is accordingly a first object of the present invention to provide a microactuator that eliminates the need to assemble individually and can be miniaturized much more than ever and, in particular, to provide a self-moved impact driven actuator which with an electrostatically driven, movable mass member in its driving source is high in environmental reliability. It is a second object of the present invention to provide a method of making such a microactuator utilizing a bulk micromachining technique.
In order to achieve the first object mentioned above, there is provided in accordance with the present invention a microactuator with an electrostatic impact driving mechanism, which as set forth in claim 1 in the appended claims comprises: a closed receptacle formed of an outer frame part, a pedestal part and a lid part; an elastic support beam member disposed in the said closed receptacle; a fixing member disposed in the said closed receptacle and securely connecting a first end of the said elastic support beam member to the said pedestal part; a movable mass member disposed in the said closed receptacle and securely connected to a second end of the said elastic support beam member; a driving electrode and a stopper member disposed in the said closed receptacle, each of which is securely connected to the said pedestal part and spacedly juxtaposed with the said movable mass member; and a power supply circuit disposed in the inside or the outside of the said closed receptacle for applying a voltage between the said movable mass and driving electrode members, wherein the microactuator is so operable that turning the said power supply circuit ON generates electrostatic attraction between the said driving electrode and movable mass members, thereby bringing the said movable member into collision with the said stopper member, followed by the transmission of a kinetic energy then produced to the said closed receptacle, and subsequently turning the said power supply circuit OFF removes the said electrostatic attraction, thereby permitting the said movable mass member to return to its original position under an elastic force exerted by the said elastic support beam member, followed by the transmission of a reaction force then produced to the said closed receptacle, whereby an entire body of the said microactuator is moved in a given direction.
The microactuator so constructed with the electrostatic driving mechanism is of a structure that can be built up by an integrated circuit process technology, and which permits the components to be integrated into an identical device, which eliminates the need to fabricate individual components, and which allows the product to be made that is extremely small in size
Specifically, the microactuator with the electrostatic impact driving mechanism may as set forth in claim 2 in the appended claims be characterized in that the said first end of the said elastic support beam member is securely connected to a single fixing element constituting the said fixing member, the said movable mass member is securely connected to the said second end of the said elastic support beam member at two places thereon, the said single fixing element is disposed so as to make the said movable mass member capable of rocking over a surface of the said pedestal part, the said driving electrode and stopper members comprise a first and a second driving electrode and a first and a second stopper member, wherein the said first driving electrode and stopper element are each disposed in front of the said movable mass member while the said second driving electrode and stopper elements are each disposed in rear of the said movable mass member, and the said voltage is applied between a said driving electrode and the said movable mass member via the said outer frame part.
In this construction of the microactuator, selecting the first or second drive electrode with which the voltage is applied allows the microactuator to be bodily moved forth or back.
Alternatively, the microactuator with the electrostatic impact driving mechanism may as set forth in claim 3 in the appended claims be characterized in that the said elastic support beam member is capable of elastically supporting the said movable mass member in two axial directions perpendicular to each other, the said elastic support beam member has a pair of first ends securely connected, respectively, to two fixing elements constituting the said fixing member, the said second end of the said elastic support beam member is securely connected at one place to the said movable mass member, the said two fixing elements are arranged so as to make the said movable mass member capable of rocking forth and back and right and left over a surface of the said pedestal part, the said driving electrode and said stopper members comprise a first, a second, a third and a fourth driving electrode and a first, a second, a third and a fourth stopper element, wherein the said first driving electrode and stopper member, the said second driving electrode and stopper member, the said third driving electrode and stopper element and the said fourth driving electrode and stopper element are disposed in front of, in rear of, at a right hand side and at a left hand side, of the said movable mass member, respectively, and the said voltage is applied between a said driving electrode and the said movable mass member via the said outer frame part.
This construction permits the microactuator to be bodily moved two dimensionally in a given plane and to be so moved in any direction as desired.
Alternatively, the microactuator with the electrostatic impact driving mechanism may as set forth in claim 4 in the appended claims be characterized in that the said movable mass member is fan-shaped and securely connected to the said second end of the said elastic support beam member, the said first end of said elastic support beam member is securely connected to the said fixing member, the said fixing member is arranged so as to make the said movable mass member capable of rocking about the said fixing member over a surface of the said pedestal part, the said driving electrode member and the said stopper member are each fan-shaped, and the said voltage is applied between the said driving electrode member and the said movable mass member via the said outer frame part.
In this construction, the microactuator is rotationally driven and may be applied to form a motor or the like.
Alternatively, the microactuator with the electrostatic impact driving mechanism may as set forth in claim 5 in the appended claims be characterized in that the said movable mass member is supported in suspension by the said elastic support beam member which obliquely support it, the said driving electrode member is disposed below the said movable mass member, the said stopper member is disposed in front or in rear of the said movable mass member, and the said voltage is applied between the said driving electrode member and the said movable mass member via the said outer frame part.
This construction of the microactuator utilizing a potential energy of gravity as the additional force provides a driving force larger in magnitude.
Alternatively, the microactuator with the electrostatic impact driving mechanism may as set forth in claim 6 in the appended claims be characterized in that the elastic support beam member has a pair of first ends securely connected, respectively, to two fixing elements constituting the said fixing member, the said second end of the said elastic support member is securely connected at one place thereon to the said movable mass member, the said two fixing elements are arranged so as to make the said movable mass member capable of rocking over a surface of the said pedestal part and are disposed in front and in rear of the said driving electrode and movable mass members, and the said voltage is applied between the said driving electrode member and the said movable mass member via the said outer frame part.
Advantageously, the said two fixing elements may be monolithic with the said outer frame part as set forth in claim 7 in the appended claims
This construction of the microactuator in which two fixing elements are used to fasten the elastic support beam member thereto allows the latter to be fixed to the outer frame part with an increased firmness and provides an improved reliability for the microactuator. Also, advantageously the fixing elements here serve as stopper members and are monolithic with the outer frame part. Thus, when the movable mass member comes into collision with the fixing elements (stopper members), electric charges on the movable mass member are advantageously transferred to the fixing elements and then absorbed by the power supply via the outer frame part. Consequently, there is no charge accumulation on the stopper members; hence there ensues a stabilized operation.
Preferably, the microactuator with the electrostatic impact driving mechanism as set forth in claim 8 in the appended claims is characterized in that the said movable mass member is securely connected to a pair of such elastic support beam members as aforesaid, which are in turn securely connected to a pair of such fixing members as aforesaid, respectively.
This construction of the microactuator permits the movable mass member to be supported as well-balanced in a horizontal plane and hence to be rocked stably and smoothly there.
Preferably, the microactuator with the electrostatic impact driving mechanism as set forth in claim 9 in the appended claims is characterized in that the said driving electrode member is split into two driving electrode elements, which are energizable independently of each other.
This construction of the microactuator utilizes a torsion effect of the elastic support beam members and thereby allows the microactuator to be advanced in a selected direction alterable, by applying a voltage only to one of the electrodes selected.
Also, the microactuator with the electrostatic impact driving mechanism may as set forth in claim 10 in the appended claims be characterized in that the said outer frame part is composed of Si single crystal, and the said pedestal and lid parts are composed of a material having a preselected friction coefficient.
Also, the microactuator with the electrostatic impact driving mechanism may as set forth in claim 11 in the appended claims be characterized in that the said material having a preselected friction coefficient is pyrex glass.
Also, the microactuator with the electrostatic impact driving mechanism may as set forth in claim 12 in the appended claims be characterized in that the said outer frame part, the said elastic support beam member, the said movable mass member, the said driving electrode member and the said stopper member are composed of a Si single crystal, and the said pedestal and lid parts are composed of a material having a preselected friction coefficient.
The present invention also provides a linear driving stage, which may a set forth in claim 15 in the appended claims comprise: a fixed platform; a movable platform slidably mounted on the said fixed platform; and a microactuator with an electrostatic impact driving mechanism as set forth in any one of claims 1 to 3 and 5 to 12, the said microactuator being fastened to the aid movable platform.
The present invention also provides a linear X-Y driving stage, which may as set forth in claim 16 in the appended claims comprise: a fixed platform; a first movable platform slidably mounted on the said fixed platform for movement in a first direction; a second movable platform slidably mounted on the said first movable platform for movement in a second direction orthogonal to the said first direction; and a microactuator with an electrostatic impact driving mechanism as set forth in any one of claims 1 to 3 and 5 to 12, the said microactuator being fastened to the said second movable platform.
The present invention also provides a drive unit which as set forth in claim 17 in the appended claims comprises a movable body and a plurality of microactuators using electrostatic impact driving mechanism incorporated therein, each of which is a microactuator as set forth in any one of claims 1 to 3 and 5 to 12.
In order to achieve the second object mentioned above, there is also provided in accordance with the present invention a method of making a microactuator with an electrostatic impact driving mechanism, by monolithically forming from a Si single crystal substrate, an outer frame part, and an elastic support beam, a movable mass, a driving electrode and a stopper member, and forming a pedestal part and a lid part from a material having a preselected friction coefficient, which method as set forth in claim 18 in the appended claims is characterized by comprising the steps of: a) forming the said driving electrode member on a front surface of the said Si single crystal substrate; b) etching the said Si substrate from its back side in order to make the said elastic support beam and movable mass members floating in the air; c) attaching a first member having a preselected friction coefficient to rear surfaces of the said Si substrate; d) etching the said Si substrate from its front side in order to form the said outer frame part, the said elastic support beam, movable mass members, the said driving electrode member and the said stopper member monolithically; e) etching the said Si substrate from its front side in order to make the said elastic support beam and movable mass members floating in the air; and f) attaching a second member having the said preselected friction coefficient to front surfaces of the said Si substrate.
The method of making a microactuator with an electrostatic impact driving mechanism may as set forth in claim 19 in the appended claims be specifically characterized in that etching steps b), d) and e) are carried out each by inductively coupled plasmaxe2x80x94reactive etching.
Also, the method of making a microactuator with an electrostatic impact driving mechanism may as set forth in claim 20 in the appended claims be specifically characterized in that steps c) and f) in which a first or second member having the preselected friction coefficient is attached to rear or front surfaces of the Si substrate are carried out each by anodic joining of pyrex glass as the first or second member to said Si substrate.